Thioredoxin reductase system mediates iron binding in IscA and iron delivery for the iron-sulfur cluster assembly in IscU
Thioredoxin reductase system mediates iron binding in IscA and iron delivery for the iron-sulfur cluster assembly in IscU
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DOI：
10.1074/jbc.m504638200
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发表时间：
2005-08-26
影响因子：
4.8
通讯作者：
Lu, JX
中科院分区：
文献类型：
--
作者：
Ding, HG;Harrison, K;Lu, JX
IscA是在细菌和真核生物中发现的铁硫簇组装机制的关键成员。以前，IscA被表征为替代的铁-硫簇组装支架，因为纯化的IscA可以宿主瞬时铁-硫簇。然而，最近的研究表明，IscA是一种铁结合蛋白，其可以为所提出的支架IscU中的铁-硫簇组装提供铁（Ding H.，克拉克河，巴西-地J.，和Ding，B.（2004）J. Biol. Chem. 279，37499 - 37504）。为了进一步阐明IscA在铁硫簇生物成因中的作用，我们重新评估了IscA在生理相关条件下的铁结合活性。结果表明，在硫氧还蛋白还原酶系统的存在下，大肠杆菌IscA在体外以2.0 x 10（19）M-1的铁结合常数结合铁。尽管硫氧还蛋白还原酶系统中的所有三种组分（硫氧还蛋白1、硫氧还蛋白还原酶和NADPH）对于介导IscA中的铁结合是必需的，但仅需要催化量的硫氧还蛋白1和硫氧还蛋白还原酶。相比之下，IscU未能结合铁的硫氧还蛋白还原酶系统的存在下，这表明IscA中的铁结合是特异性的。然而，硫氧还蛋白还原酶系统可以促进铁-硫簇组装在IscU的存在下的铁负载的IscA，半胱氨酸脱硫酶（IscS），和L-半胱氨酸，证明了生理相关的系统的铁-硫簇的生物成因。结果为IscA能够募集细胞内“游离”铁并将铁递送用于IscU中的铁-硫簇组装的假设提供了额外的证据。
IscA is a key member of the iron-sulfur cluster assembly machinery found in bacteria and eukaryotes. Previously, IscA was characterized as an alternative iron-sulfur cluster assembly scaffold, as purified IscA can host transient iron-sulfur clusters. However, recent studies indicated that IscA is an iron-binding protein that can provide iron for the iron-sulfur cluster assembly in a proposed scaffold IscU ( Ding H., Clark, R. J., and Ding, B. ( 2004) J. Biol. Chem. 279, 37499 - 37504). To further elucidate the roles of IscA in the biogenesis of iron-sulfur clusters, we reevaluate the iron binding activity of IscA under physiologically relevant conditions. The results indicate that in the presence of the thioredoxin reductase system, Escherichia coli IscA binds iron with an iron association constant of 2.0 x 10(19) M-1 in vitro. Whereas all three components (thioredoxin 1, thioredoxin reductase and NADPH) in the thioredoxin reductase system are essential for mediating the iron binding in IscA, only catalytic amounts of thioredoxin 1 and thioredoxin reductase are required. In contrast, IscU fails to bind iron in the presence of the thioredoxin reductase system, suggesting that the iron binding in IscA is specific. Nevertheless, the thioredoxin reductase system can promote the iron-sulfur cluster assembly in IscU in the presence of the iron-loaded IscA, cysteine desulfurase ( IscS), and L-cysteine, demonstrating a physiologically relevant system for the biogenesis of iron-sulfur clusters. The results provide additional evidence for the hypothesis that IscA is capable of recruiting intracellular "free" iron and delivering the iron for the iron-sulfur cluster assembly in IscU.